1. Field of the Invention
The present invention relates generally to valves, and more particularly to an electrical drive apparatus for valves.
2. Description of the Related Art
In the field of valves, various electrically opened/closed valves controlled by electrical drive apparatuses have been developed instead of traditional manually operated valves for saving time and convenience. The electrical drive apparatuses serve to control opening/closing of the valves such as ball valves, butterfly valves or other types of valves.
However, when a valve body needs to be urgently closed in an emergency, while a blackout or a power cut unfortunately coincidentally takes place, it is still necessary to switch the valve body to a manual operation mode to manually operate/control the valve body.
For example, U.S. Pat. No. 4,994,001 discloses a structure for switching the valve body between an electrical drive mode and a manual drive mode.
However, the structure of U.S. Pat. No. 4,994,001 still has a shortcoming as follows: In case that a power cut or other special incident takes place and it is necessary to manually open or close the valve body, an operator needs to turn a hand wheel 16 to drive a worm 26 and a spiral gear 28. The spiral gear 28 then drives a transmission shaft 60 to control the valve body. Accordingly, it takes quite a lot of time for the operator to close or open the valve body. In general, there are numerous valve bodies in a working site. As a result, the operator is often exhausted after closing or opening all the valve bodies.